William m



UNITED STATES 4 PATENT OFFICE.

WILLIAM M. THOM, OF ST. LOIS, MISSOURI, ASSIGNOR OF ONE-HALF TO JOHN F. MASON, OF" SAME PLAGE.

DRAFTING IMPLEMENT.

SPECIFICATION forming part of Letters Patent No. 268,749, dated December 5, 1882.

Application filed May 3, 1882. (No model.)

To all whom tt may concern Be it known that'I, WILLIAM M. THOM, of St. Louis,in the county of St. Louis and State of Missouri, have invented a new and useful 5 Improvement in Drafting-Instruments; and I do hereby declare that the following is a full, clear, and exact description f the same.

My invention relates to that class of drawing instruments of the kind known as T- 1o squares; and it consistsin the peculiar combination and arrangement ot' a T-square, a pivoted blade having a registering-protractor, an index-hand, and a special clamping device, the whole forming a simple, easily-constructed, and accurate instrument for general drafting, and particularly for the purpose of accurately adjusting the instrumentto any required angle and holding it there firmly.

Heretofore complicated and expensive dra ftzo ing implements have been provided, by which these objects have been accomplished, but their expense and the care which must be observed in their use has restricted their employment to the liner kinds of work, so that the need which has long existed for a simple and cheap instrument which couldbe made and sold at the price of .an ordinary Tsquare has not yet been supplied.

To meet these requirements is the object of 3o the invention illustrated in the accompanying drawings, in which- Figure l is a plan View of the device. Fig. 2 an end View, showing the cam fastening 0r lockingdeviee. Fig. 3 is a section through the pivot.

In the drawings, A is an ordinary blade or straight-edge, preferably made of wood, but adapted to be made of metal, if desired. To this blade is secured by theV ordinary mortise- 4o joint the fixed head B, the two parts, when in place, presenting the appearance of an ordinary draftsmans T-square.

C is a movable head, of ahoutthe same width and length as the head B,'and this part C has rigidly attached to or forming an integral part of it a registering protractor, D, having a fixed scale numbered from zero in the center in both directions to ninety degrees, a segment of the semicircular portion projecting 5o beyond thevxcd head when the two heads are in line. The head U and protractor D are pivoted to the xed head B by a central bolt,

1, passing through both the fixed and movable heads, and having a washer, 2, which bears on the lower face of the movable head. On the upper end of the holt l is a thumb-nut, 3, having a broad base or bearing-surface, 4, provided with an offset, 5. .Ihe bearing-surface 4 is slightly inclined, as shown in Fig. 2, to travel on the correspondingly-inclined surface 6o of a plate, 6, firmly secured to the fixed head B of the T-square, such plate also havinga stop or offset, 7.

The thumb-nut, pivoted bolt, and inclinedl plate are preferably constructed of metal, though hard wood may be used, if desired.

A stationary pointer Vor index-hand is secured to the fixed head B, which projects out to theprotractor-scale and indicates the angle at which the movable head is turned. o

In the operation of the device the head C` is turned on the pivot in either direction until the hand or pointerindicates the proper angle. The thumbnut is at this point turned to the right,wedging the inclines and drawing the parts tightly together. The movable head is then used in the same manner as the fixed head in an ordinary T-square.

In mechanical drawing, where much section-shading or cross-hatching77 is required, 8o draftsmen are commonly forced to depend entirely upon the correctness of their eye for the accuracy and parallelism of the necessary lines. By my device correctness is assured solongas the proper angle has been given and the movable head bears truly on the edge of the drawing-board.

This device is not intended to supply the place ofthe expensive and delicate instruments which are necessary for some kinds of work; 9o butas a simple, convenient, and efficient instrument for the ordinary use of draftsmen it possesses advantages which will be readily appreciated by those skilled in the art. There is also great convenience in numbering the protractor-scale from the zro-pointin both directions, since the blades may be readily set in opposite directions, though at the sameangle, if necessary.

It will he of course understood that the en. roo

tire device may be made of metal instead of Wood, and may be finished in any style commonly employed in the higher vclass of' draft# ingimplements.

1 am `aware of the patents of Card of 1842 and of Hoerman of 1881, and I disclaim t-he inventions therein set forth,'the novelty of my device consistngo'f a novel and complete .combination of essential elements not found in either of said patents. e

Having thus described my invention, what I claim is- A A drawing implement consisting of a blade,

...A, having aiixed head, B, a pvot'ed movable blade, C, having a registeringprotractor, D, a 15 Xed hand on the head B, and a clamping device consisting of a thumb-nut having thein'- clined bearing-surface 4, and the plate 6, having an opposing incline, all substantially as described, and as a complete article of manufaczo ture.

In testimony whereofIhave signed my name to this specification in presence of two subscrib- 

